1. Field of the Invention
The present invention relates to an illumination optical apparatus, wherein a light source system providing an illumination light includes an ellipsoidal mirror, and a projection type display apparatus using the same.
2. Description of the Related Art
For example, an illumination optical apparatus used in a projection type display apparatus (projector), etc. provided with a liquid crystal display device is configured to include a pair of fly-eye lenses.
In such an illumination optical apparatus including a pair of fly-eye lenses, the pair of fly-eye lenses uniformize (equalize) a light intensity distribution of an illumination light from a light source and emit to an illumination surface of, for example, a liquid crystal display panel functioning as a spatial light modulation device, etc.
The following publications disclose such a projection type display apparatus and an illumination optical apparatus.
The Japanese Unexamined Patent Publication (kokai) No. 2000-241878-A discloses a projection type display apparatus using a light source composed of a paraboloidal reflector and a lamp, capable of obtaining higher screen illumination by arranging a condenser lens in front of the paraboloidal reflector.
The Japanese Unexamined Patent Publication (kokai) No. 2000-221585-A discloses an apparatus having a light source set to have a cathode displaced to the opening side by a predetermined distance (particularly, refer to FIG. 2).
The Japanese Unexamined Patent Publication (kokai) No. 7-161601-A discloses an illumination optical apparatus including a fly-eye integrator, wherein a stop is provided on an incident surface and emission surface of the fly-eye integrator and the fly-eye integrator is movable in an optical axis direction.
An illumination optical system in the apparatuses explained above is basically composed of an ellipsoidal mirror, a light source for emitting a light by discharging due to a direct current between positive and negative electrodes, and a collimator lens for collimating a light flux converged by the ellipsoidal mirror to an approximately parallel light flux, when the ellipsoidal mirror and the collimator lens are arranged to have an identical focal point. The stop is arranged at the second focal point of the ellipsoidal mirror.
However, in the above illumination optical apparatus, the ellipsoidal focal point and the collimator lens focal point are brought to be identical to obtain a parallel light flux when the light source is sufficiently small to be deemed as a point source, but in the case of a high output lamp, the electrode interval is wide, so that when it is handled as a point source, an optimal illumination efficiency cannot be obtained. Furthermore, in the case where a direct current lighting is carried out, since a highest-intensity luminous point exists close to one electrode, a center of the brightness distribution is deviated from the midpoint of the electrodes and the distribution becomes uneven.